Wegener's granulomatosis (WG), polyarteritis with glomerulonephritis (so-called microscopic polyarteritis), and idiopathic necrotizing and crescentic glomerulonephritis are a triad of diseases with a high incidence of morbidity and mortality. Approximately 40-50 patients suffering from these diseases are admitted annually to the Massachusetts General Hospital. The renal glomerular lesions in these conditions are usually indistinguishable, and are characterized histologically by focal, segmental necrosis of the tufts, fibrinoid deposits, as well as variable degrees of proliferation, leukocyte infiltration, destruction of the glomerular basement membranes which together, can rapidly lead to renal failure. Diagnostic tests that can distinguish between these conditions and other diseases with similar manifestations, or that are useful for monitoring disease activity, are lacking. Recently several groups, including our own, have identified circulating autoantibodies directed against several cytoplasmic constituents of granulocytes and mononuclear phagocytes in a high percentage of patients with active disease; the titers usually regress upon institution of immunosuppressive therapy. Detection of these autoantibodies has generally been made by indirect immunofluorescence, using ethanol-fixed normal human granulocytes as substrates and a fluorescein-labelled anti-human IgG as secondary antibody. Although detection of the autoantibodies has been useful in diagnosis and monitoring disease activity, several problems remain with respect to sensitivity, quantitation, and identification of relevant antigens. One antigen is myeloperoxidase, a granulocyte enzyme with anti-microbial and cytotoxic potential. In other patients, especially those with WG, autoantibodies against a 29kD protein (p29) are found. Preliminary evidence indicates that in still other patients autoantibodies may be directed against a 55kD protein (p55). The nature and function of p29 and p55 are unknown. We have recently generated murine monoclonal antibodies against myeloperoxidase, p29 and p55. We also purified p29 by affinity chromatography. We propose to elucidate the primary structure of p29 and p55 using immunochemical and molecular biology techniques. The pathogenic role of the autoantibodies is unknown. It is possible that they have a pathogenic effect by mediating granulocyte activation or that they potentiate the toxic effects of the antigens with which they react. The injurious effects of p29, p55, and myeloperoxidase in the presence and absence of autoantibodies will be determined using cells often involved in the early lesions of vasculitis, namely granulocytes and endothelial cells. In addition, the nature of the epitopes recognized by the autoantibodies will be determined. The significance of the information derived, will not only be crucial for characterization of the structure of a novel group of granulocyte proteins and their role in normal granulocyte biology, but will also enhance our understanding of the pathogenesis of a group of systemic vascular disorders responsible for a major portion of rapidly progressive necrotizing and crescentic glomerulonephritis. Structural characterization of these antigens may also make it possible to generate specific reagents that will improve the diagnostic potential of currently available methods of detecting the autoantibodies.